#2186 - Add `IS_NULL` check during string variable initialization
#2186 - Add `IS_NULL` check during string variable initialization

vpg/zephir,phalcon/zephir,phalcon/zephir,zephir-lang/zephir,vpg/zephir,phalcon/zephir,phalcon/zephir,vpg/zephir,zephir-lang/zephir,vpg/zephir,phalcon/zephir,phalcon/zephir,vpg/zephir,zephir-lang/zephir,vpg/zephir,zephir-lang/zephir,zephir-lang/zephir